The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
An aircraft is moved by several turbojet engines each housed in a nacelle. The nacelle generally has a tubular structure comprising an air intake upstream from the turbojet engine, a middle section designed to surround a fan of the turbojet engine, a downstream section housing the thrust reverser means and designed to surround the turbojet engine combustion chamber, and generally ends with a jet nozzle situated downstream from the turbojet engine.
This nacelle is designed to house a dual flow turbojet engine capable of using the rotating fan blades to generate a hot air flow, coming from the combustion chamber of the turbojet engine, and a cold air flow that circulates outside the turbojet engine through an annular channel that is called the tunnel.
During landing of the aircraft, the thrust reverser device is designed to improve the braking capacity thereof by reorienting at least part of the thrust generated by the turbojet engine forward.
In this phase, the thrust reverser device obstructs the cold air flow tunnel and orients the latter flow toward the front of the nacelle, thereby generating a counterthrust that is added to the braking of the wheels of the aircraft, the means implemented to perform this reorientation of the cold air flow varying depending on the type of reverser.
In general, the structure of a reverser comprises a reverser cowl movable between a deployed position, in which it opens a passage in the nacelle designed for the deflected air flow, on the one hand, and a retracted position, in which it closes the passage, on the other hand.
In the case of a cascade reverser, the reorientation of the flow of air is done by cascade vanes, associated with reverser flaps, the cowl serving only to slide so as to expose or cover said cascade vanes. The reverser flaps form blocking doors that can be activated by the sliding of the cowl, causing closing of the tunnel downstream from the vanes, so as to optimize the reorientation of the cold air flow. In a known manner, the cascade vanes are attached to the casing of the turbojet engine and the middle section of the nacelle using a front frame.
Also known are thrust reversers in which the cascade vanes are movable and translate with the reverser cowl during thrust reversal phases.
Irrespective of the type of reverser, a recurring problem is that the dimensions of the nacelle and the associated cowl are too large.
In fact, the length of the vanes necessary for the flow deflection is determined by the flow passing through the tunnel.
For dual flow turbojet engine nacelles with high dilution rates, this means that the length of the vanes must be considerable.
Due to aerodynamic constraints, they also occupy a certain volume inside the thrust reverser cowl, which can create significant dimensions of the thrust reverser cowl and the nacelle.
There is thus a need to limit the dimensions of the cowl and the nacelle and, consequently, to reduce the mass and the aerodynamic drag of the latter.
One of the well-known advantages of thrust reversers in which the cascade vanes are movable is to reduce the axial length of the nacelle and the associated cowl, causing a reduction in the mass and drag.
Furthermore, aside from its thrust reversal function, the reverser cowl belongs to the rear section of the nacelle and has a downstream part forming the jet nozzle aiming to channel the discharge of the airflows.
The optimal section of the jet nozzle may be adapted based on different flight phases, i.e., the takeoff, ascent, cruising, descent, and landing phases of the aircraft. It is associated with an actuating system making it possible to vary and optimize its section as a function of the flight phase of the aircraft at that time. The variation of that section, illustrating the section variation of the cold air flow tunnel, is done by partial translation of the reverser cowl.
A device is known according to document U.S. Pat. No. 5,655,360, which describes a thrust reverser with fixed cascade vanes comprising a moving cowl forming a jet nozzle in its downstream part, the thrust reverser being provided with a device making it possible to vary the section of the nozzle so as to preserve an optimal configuration based on the flight phases.
The already well-known advantages of variable section nozzles are in particular the reduction in noise or decrease in fuel consumption.